sme: Core file support for Linux

This patch enables dumping SME state via gdb's gcore command and also
enables gdb to read SME state from a core file generated by the Linux
Kernel.

Regression-tested on aarch64-linux Ubuntu 22.04/20.04.

Reviewed-by: Thiago Jung Bauermann <thiago.bauermann@linaro.org>

2 files changed, 49 insertions, 0 deletions

diff --git a/gdb/arch/aarch64-scalable-linux.c b/gdb/arch/aarch64-scalable-linux.c
index 3803acf..2e4aa92 100644
--- a/gdb/arch/aarch64-scalable-linux.c
+++ b/gdb/arch/aarch64-scalable-linux.c
@@ -19,3 +19,37 @@
    along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
 
 #include "arch/aarch64-scalable-linux.h"
+#include "arch/aarch64.h"
+#include "gdbsupport/byte-vector.h"
+#include "gdbsupport/common-regcache.h"
+
+/* See arch/aarch64-scalable-linux.h  */
+
+bool
+sve_state_is_empty (const struct reg_buffer_common *reg_buf)
+{
+  /* Instead of allocating a buffer with the size of the current vector
+     length, just use a buffer that is big enough for all cases.  */
+  gdb_byte zero_buffer[256];
+
+  /* Zero it out.  */
+  memset (zero_buffer, 0, 256);
+
+  /* Are any of the Z registers set (non-zero) after the first 128 bits?  */
+  for (int i = 0; i < AARCH64_SVE_Z_REGS_NUM; i++)
+    {
+      if (!reg_buf->raw_compare (AARCH64_SVE_Z0_REGNUM + i, zero_buffer,
+				 V_REGISTER_SIZE))
+	return false;
+    }
+
+  /* Are any of the P registers set (non-zero)?  */
+  for (int i = 0; i < AARCH64_SVE_P_REGS_NUM; i++)
+    {
+      if (!reg_buf->raw_compare (AARCH64_SVE_P0_REGNUM + i, zero_buffer, 0))
+	return false;
+    }
+
+  /* Is the FFR register set (non-zero)?  */
+  return reg_buf->raw_compare (AARCH64_SVE_FFR_REGNUM, zero_buffer, 0);
+}
diff --git a/gdb/arch/aarch64-scalable-linux.h b/gdb/arch/aarch64-scalable-linux.h
index df17410..cb9d85a 100644
--- a/gdb/arch/aarch64-scalable-linux.h
+++ b/gdb/arch/aarch64-scalable-linux.h
@@ -22,6 +22,7 @@
 #define ARCH_AARCH64_SCALABLE_LINUX_H
 
 #include "gdbsupport/common-defs.h"
+#include "gdbsupport/common-regcache.h"
 
 /* Feature check for Scalable Matrix Extension.  */
 #ifndef HWCAP2_SME
@@ -35,4 +36,18 @@
 /* Mask including all valid SVCR bits.  */
 #define SVCR_BIT_MASK (SVCR_SM_BIT | SVCR_ZA_BIT)
 
+/* SVE/SSVE-related constants used for an empty SVE/SSVE register set
+   dumped to a core file.  When SME is supported, either the SVE state or
+   the SSVE state will be empty when it is dumped to a core file.  */
+#define SVE_CORE_DUMMY_SIZE 0x220
+#define SVE_CORE_DUMMY_MAX_SIZE 0x2240
+#define SVE_CORE_DUMMY_VL 0x10
+#define SVE_CORE_DUMMY_MAX_VL 0x100
+#define SVE_CORE_DUMMY_FLAGS 0x0
+#define SVE_CORE_DUMMY_RESERVED 0x0
+
+/* Return TRUE if the SVE state in the register cache REGCACHE
+   is empty (zero).  Return FALSE otherwise.  */
+extern bool sve_state_is_empty (const struct reg_buffer_common *reg_buf);
+
 #endif /* ARCH_AARCH64_SCALABLE_LINUX_H */